Portable travel pillows and head rests are known generally. Some of these devices are specifically devised to attach to the backs of seats to provide lateral support for the head of a seated person.
The following patent documents are believed to be representative of the current state of the prior art in this field: U.S. Pat. No. 6,592,184, issued Jul. 15, 2003, U.S. Patent App. Pub. No. US 2002/0163240, published Nov. 7, 2002, U.S. Patent App. Pub. No. US 2007/0056111, published Mar. 15, 2007, U.S. Patent App. Pub. No. US 2007/0180623, published Aug. 9, 2007, U.S. Pat. No. 5,317,772, issued Jun. 7, 1994, U.S. Pat. No. 5,471,690, issued Dec. 5, 1995, U.S. Pat. No. 5,544,378, issued Aug. 13, 1996, U.S. Pat. No. 6,641,221, issued Nov. 4, 2003, U.S. Pat. No. 6,684,429, issued Feb. 3, 2004, U.S. Pat. No. 6,708,355, issued Mar. 23, 2004, U.S. Pat. No. 6,942,297, issued Sep. 13, 2005, U.S. Patent App. Pub. No. US 2007/0209115, published Sep. 13, 2007, U.S. Pat. No. 6,017,094, issued Jan. 25, 2000, U.S. Pat. No. 6,394,554, issued May 28, 2002, U.S. Design Pat. No. D522,300, issued Jun. 6, 2006, U.S. Design Pat. No. D534,389, issued Jan. 2, 2007 and UK Patent App. GB 2 440 906, published Feb. 20, 2008.